Do humans have anything to do with climate change?

1 Answer
Dec 20, 2015

The world's leading climate scientists have unequivocally determined climate change is caused by human activities.


The fifth report from the Intergovernmental Panel on Climate Change, in which leading climate scientists from across the globe meet and discuss climate change, stated with 95% certainty that climate change (and global warming) is caused by humans.

There is no debate among scientists who study climate science that our current rates of warming are human-caused. 97% of scientists actively research climate change believe it is caused by human activities (Cook et al., 2013).

Increases in greenhouse gases such as carbon dioxide (CO2) result in the atmosphere retaining more heat. This retention of heat in the atmosphere causes the planet to experience warmer global temperatures on average.

Levels of carbon dioxide in the atmosphere have risen significantly since the industrial revolution. In the image below, we see CO2 levels in the atmosphere have been relatively stable until the amount emitted by humans increases.

If you're not convinced by the above data and believe that increase in atmospheric CO2 could still be naturally caused, there's even more evidence to the contrary. If we look at the levels of oxygen in the atmosphere, we would expect to see lower levels of oxygen if humans are burning CO2. This is evidence that human activity is directly linked to increase levels of CO2 in the atmosphere. To learn more about this process, click here.

A second piece of indisputable evidence is the ratio of carbon isotopes. Fossil fuels have lower 13C/12C ratios than the atmosphere does. Yet around 1850, when we begin to see a rise in atmospheric CO2 levels, we also see a decrease in the ratio of 13C/12C in the atmosphere, providing further evidence that fossil fuels humans are putting into the environment are causing increases in CO2 levels.

The question of whether or not this is man made or not always comes up. Here is something to consider. When Krakatoa erupted back in 1871, it changed the global climate for a few years. The climate went back to normal only after the material from the eruption fell out of the atmosphere due to gravity. Now granted the effect of volcanic ash is much much greater than the effect of carbon dioxide, BUT the mass of all the volcanic ash from Krakatoa is the same mass as the carbon that humans put into the atmosphere every 3-4 months. And the carbon we put into the atmosphere isn't being removed by gravity.

To read more, check out NASA's article, Skeptical Science's article, and the EPA's answers to FAQs.


J. Cook, et al, "Quantifying the consensus on anthropogenic global warming in the scientific literature," Environmental Research Letters Vol. 8 No. 2, (June 2013); DOI:10.1088/1748-9326/8/2/024024